Linear low and medium density polyethylene copolymers (LLDPE) are widely used commercially in films which are conventionally prepared by blown film extrusion. Such films have generally good properties, but often exhibit undesirably low stiffness for many uses. It is also desirable to obtain blends of these polymers which require less power to extrude and which can be extruded through a narrower die gap.
U.S. Pat. No. 4,565,847 having the same assignee as herein, describes films of LLDPE, polypropylene and ethylene-propylene rubbers having improved stiffness and good tear strength.
Similarly, improvements in MD tear strength and stiffness of films are obtained by blending small amounts of polystyrene (up to about 10 weight percent) with LLDPE as described in U.S. Pat. No. 4,579,912. Higher amounts of polystyrene in excess of about 10 weight percent causes drastic loss of tear strength.
In accordance with this invention both polystyrene (PS), or other aromatic polymer, and polypropylene are blended with LLDPLE to give films with a high modulus and with better tear strength than can be obtained with LLDPE/PP or LLDPE/PS blends. At the same time, better processing characteristics are achieved.